1. Field of the Invention
The present invention relates to a process for chemical logging or diagraphy of a liquid, as well as to a chemical logging or diagraphy installation for performing said process. More specifically, said chemical logging process makes it possible to remove samples of liquid or water from a borehole, an ocean, a lake or a river and perform measurements thereon, in order to establish concentration profiles of at least one chemical element in said liquid. This process makes it possible to e.g. follow on a day to day basis the evolution of a pollution spill present in the ocean.
2. Discussion of the Related Art
In order to establish concentration profiles of chemical elements present in the water of a well or in the open water, the prior art already discloses a spot sampling procedure consisting of using a sampling bottle operated by a cable. These bottles are generally constituted by a cylinder open at its two ends and which is lowered to the requisite depth and remotely sealed. These bottles are sealed by an electrical or mechanical device. Thus, e.g. the sealing of the bottle can be obtained by means of a messenger, which is a type of counterweight or metal weight which is allowed to slide by gravity along the cable and which triggers the closing of a valve by its impact on a closing mechanism. The chemical measurements are subsequently performed in the laboratory on the samples taken. At present numerous bottle types exist meeting various demands with regards to the sampling volume, the materials forming the sampling bottle, the principle of initiating or triggering the same, the retention or not of the sampled dissolved gases, the filtration or the maximum pressure of use.
Such spot sampling processes take a long time to carry out, because it is a question of lowering and then raising again the said sampling bottle for each sample. In addition, in order to obtain a detailed concentration profile or for seeking a very localized anomaly, it is necessary to take a large number of samples.
A device is also known making it possible to perform multiple sampling operations and having on the same cable several sampling bottles designed so as to open and then close again in an automatic manner and simultaneously once the complete cable has been unrolled into the liquid mass to be analyzed.
Although this procedure speeds up the sampling operations it is not any more accurate, because the distance between two sampling bottles is frequently inadequate to obtain a very precise concentration profile or an anomaly passes through the reading made. Moreover, for a given sampling pass (i.e. the height over which the removal corresponding to a sample takes place), each sample is not necessarily representative of the mean concentration on the pass in question.
Finally, devices for in situ measurement are known comprising a specific probe for one or more chemical elements and which make it possible to perform a direct depth measurement at the sampling location and return the collected informations to the surface by means of an electric cable. These probes are e.g. spectral gamma probes for gamma emitters making it possible to e.g. measure iodine quantities.
However, these probes are generally very complex and costly, because they require the installation of an electronic device within a tight body and must be able to withstand pressure stresses. These probes are generally specific to one or several elements and their performance characteristics are limited. Finally, frequently, they are less accurate than a laboratory bench-type installation. The stresses to which said probes are exposed generally lead to a resolution loss and to interference phenomena.